A major earthquake – the Big One – is statistically almost certain in California in the coming decades, and there is even worse news below the ground: it is likely to be followed by a series of similar-sized temblors, according to a leading seismologist.

The current relatively quiet seismic period – in which “far less” energy is being released in earthquakes than it is being stored from tectonic plate motions “cannot last forever,” said University of Southern California earth sciences professor James Dolan while delivering a new paper during the Seismological Society of America conference in Pasadena.